Electrolytic process for the preparation of olefine oxides



United States Patent 3,451,905 ELECTROLYTIC PROCESS FOR THE PREPA- RATION 0F OLEFINE OXIDES Walter Kriinig and Johann Grolig, Leverkusen, Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany No Drawing. Filed Mar. 1, 1966, Ser. No. 530,788 Claims priority, applicF: 1tion4(1 ermany, Mar. 4, 1965,

45, 6 Int. Cl. C07d 1/08; B01k 3/02, 3/10 US. Cl. 204-80 10 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for the preparation of olefine oxides.

It is known to prepare olefine oxides from olefines by an electrochemical process in which an aqueous solution of a metal halide is electrolysed in an electrochemical system in which the olefine is introduced into the reaction near the anode and the primarily formed halohydrin is then dehydrohalogenated in an electrochemical system with formation of the olefine oxide (cf. Belgian patent specification 637,691 and French patent specification 1,375,973). In particular, the process is carried out in that the electrolyte is transferred from the anode chamher into the cathode chamber through a diaphragm and olifine halohydrin is formed by electrochemical action from the olefine introduced into the anode chamber, and this olfine halohydrin, dissolved in the electrolyte, is transported through the diaphragm and is converted into olefine oxide in the cathode chamber due to the alkalinity in the cathode chamber. Several of the aforesaid systems consisting of an anode, a diaphragm and a cathode can be combined to form a cell aggregate.

In this known process, the diaphragm which separates the anode chamber from the cathode chamber may be made of an inert permeable or porous material such as asbestos, Teflon, polyethylene etc.

It has now been found that the electrochemical preparation of olefine oxides from olefines in a system consisting of an anode, a cathode and a diaphragm situated between, using an aqueous electrolyte and introducing the olefine near the anode, can be carried out particularly advantageously if the diaphragm used is a web of woven polyacrylonitrile fibres.

The web may be made exclusively from monofils or it may be made from yarns produced from endless filaments or staple fibres. Different forms of polyacrylonitrile fibres may be used in the warp and weft, e.g. the warp may be made of monofils and the weft of yarn spun from fibres. Suitable thicknesses for the fabric of the diaphragm are for example 0.1 to 1.5 mm., especially 0.2 to 1 mm. It may be advantageous to shrink the fabric by heat before it is used in accordance with the invention. Furthermore, the fabric may be subjected to a swelling process before it is used, for example with the use of organic solvents, e.g. those formed in the course of the electrochemical process.

The fabrics used according to the invention may be made of pure polyacrylonitrile or of copolymers containing at least of bound acrylonitrile. The remaining constitutents may consist of the usual components used for copolymerisation, e.g. vinyl acetate or methyl acrylate.

It is advantageous to bring the diaphragm of polyacrylonitrile fabric as close to the cathode as possible. In a preferred form the cathode is a wire mesh and the polyacrylonitrile fabric is adhered to it. When used as diaphragms, these polyacrylonitrile fabrics are distinguished by great stability, both as regards the constancy of the operating results and as regards the chemical and mechanical resistance. The polyacrylonitrile fabric can be produced very uniformly and hence provides a diaphragm which is uniform in its permeability over its whole surface. This factor also contributes to the advantageous effect.

As mentioned before it is known that abestos may be used as a diaphragm for the process of the invention. In practical use the asbestos proves to be unsatisfying since the asbestos fibers can be used only for a short period of time since the separation of the cathode chamber and anode chamber is insufiicient after a few days. This causes a recirculation between both chambers which leads to a formation of by-products such as glycol.

If other diaphragm materials are used, e.g. materials from polyethylene or fiuor hydrocarbons the na similar effect is noticed since these materials are insufficient to withstand the mechanical stress to which they are subjected. Furthermore these materials have the disadvantages that they are not sufficiently wettable which is of importance for the passage of current.

It was surprising that the polyacrylonitrile fiber materials could be used for the process of the invention since it was to be expected that the nitrilo groups would be saponified in the very strong alkaline medium which occurs at the cathode. It has been found that very surprisingly the diaphragms of the invention are very durable for long reaction times.

Suitable materials for use in the preparation of the olefine oxides are in particular gaseous Inonoolefines such as ethylene, propylene and butylene as well as halogenated monoolefines, for example allyl chloride. Aqueous solutions of sodium chloride or potassium chloride or mixtures thereof may for example be used as electrolyte. The concentration of the salts in the electrolytes may be, for example, 2 to 20% and preferably 3 to 15%. The anodes and cathodes may be rectangular and placed parallel to each other. The anode should preferably be porous so that the gaseous raw material introduced can pass through the pores of the anode into the anode chamber. On the other hand, the gaseous olefines may be introduced through a frit or similar distributor means arranged below the anode. Other methods of introducing the olefines may also be employed provided they ensure fine distribution of the gas in the anolyte.

A suitable material for the anode is, for example, graphite, but platinum-plated titanium may also be used. The aqueous electrolyte is introduced into the anode chamber and transferred through the diaphragm and the cathode into the cathode chamber, the electrolyte being transferred at a rate of between and 100 cc./min. through 1 square decimetre of the cathode surface. The catholyte leaving the cathode chamber may be freed from the olefine oxide contained in it, e.g. by distillation, and returned to the anode chamber, thereby completing the cycle. When by-products formed in the course of electrolysis have accumulated to a certain concentration in the circulating electrolyte, it is advantageous to remove a part of the electrolyte from the cycle and replace it by fresh electrolyte. The process may be carried out e.g. with current densities of 2 to 50 amp/100 cm. of electrode surface, voltages of 3.2 to 5 volts and temperatures of to 90 C. It is advantageous to work at ordinary pressure but a slightly elevated pressure may be employed. The rate of throughput of olefine through the anode chamber is preferably so chosen that 5 to 95% of the olefine is converted in a single passage through the chamber.

It is also possible to arrange that the anolyte charged with halohydrin is reacted outside the cell with the catholyte to form the olefine oxide and that the reacted mixture of anolyte and catholyte is reintroduced into the anode and cathode chamber respectively.

The following examples illustrate the invention:

EXAMPLE 1 An electrolytic cell containing a porous graphite anode having an area of 150 cm. and a wire mesh cathode of the same surface area arranged opposite it is used. A cloth of polyacrylonitrile fabric made from threads of a thickness of 0.2 mm. was applied to the cathode on the side facing the anode. The entire thickness of the cloth was 0.5 mm. The electrolyte was a 9.3% solution of common salt. This was passed from the anode chamber into the cathode chamber through the diaphragm at a rate of 2 l. per hour. The temperature of the electrolyte was 52 C. The operation was carried out at ordinary pressure and a voltage of 3.5 volts between anode and cathode. Propylene was passed through the porous anode at the rate of l. per hour. 20% of this propylene was converted and 80% left the anode chamber in a gaseous state. The electrolyte passed through the diaphragm and the cathode, and the propylene chlorohydrin formed in the anode chamber and dissolved in the electrolyte was converted into propylene oxide in the cathode chamber. The catholyte contained 0.35% of propylene oxide. The propylene oxide dissolved in the catholyte can easily be recovered from the electrolyte by distillation before the electrolyte is returned to the anode chamber.

EXAMPLE 2 An electrolytic cell having an anode of 175 cm. of

titanium sheet covered with a thin layer of platinum was used. Opposite the anode was a wire mesh cathode of the same surface area. On the side of the cathode facing the anode was applied a cloth of polyacrylonitrile fabric made from threads of 0.2 mm. in thickness. The total thickness of the cloth was 0.5 mm. In the anode chamber of the cell, a frit plate of ceramic material was arranged below the anode, through which plate the olefine that was to be reacted was introduced in a finely divided form into the anode chamber. The electrolyte was a 5% aqueous potassium chloride solution. This was passed from the anode chamber into the cathode chamber through the diaphragm at the rate of 2 l. per hour. The temperature of the electrolyte was 52 C. Normal pressure was employed. 25 l. of propylene were passed per hour through the frit. 20% of this propylene underwent reaction and left the anode chamber in the gaseous state. The electrolyte passed through the diaphragm and the cathode, and in the cathode chamber the propylene chlorohydrin, formed in the anode chamber and dissolved in the electrolyte, was converted into propylene oxide. The catholyte contained 0.42% of propylene oxide. The current yields of main products and by-products were as follows.

Product: Current, percent Propylene oxide 87.7

EXAMPLE 3 The electrolytic cell described in Example 2 was used. The current density was 11.1 amp./ cm. The electrolyte was a 5% aqueous potassium chloride solution. This was passed at the rate of 4.1 per hour from the anode chamber to the cathode chamber through the diaphragm. The temperature of the electrolyte was 52 C. Ordinary pressure was employed. Ethylene was charged through the frit at the rate of 45 l. per hour. 20% of this ethylene was converted and 80% left the anode chamber in a gaseous state. The electrolyte passed through the diaphragm and the cathode, and the conversion of the ethylene chlorohydrin formed in the anode chamber and dissolved in the electrolyte into ethylene oxide took place in the cathode chamber. The catholyte contained 0.3% of ethylene oxide. 82% of the total current yield was ethylene oxide, 8% ethylene chlorohydrin and 6% dichloroethane.

EXAMPLE 4 The electrolytic cell described in Example 2 was used under the experimental conditions described in Example 3. A gaseous mixture consisting of 50% allyl chloride and 50% nitrogen was introduced into the anode chamber through the frit at the rate of 45 l. per hour. 40% of the allyl chloride was converted, 60% left the anode chamber in the gaseous state. The electrolyte passed through the diaphragm and the cathode, and in the cathode chamber the propylene-dichlorohydrin formed in the anode chamber and dissolved in the electrolyte was converted into epichlorohydrin. The catholyte contained 0.55% of epichlorohydrin and the total current yield of epichlorohydrin was 70% What we claim is:

1. In the process for electrochemically converting an olefin to olefin oxide in which an electric current is passed from a cathode to an anode through an aqueous electrolyte and the olefin to be converted is introduced into the electrolyte adjacent the anode, the improvement which comprises maintaining a diaphragm of polyacrylonitrile fibers in the electrolyte separating the anode from the cathode during the electrochemical conversion.

2. A process as claimed in claim 1 in which the thickness of the fabric of the diaphragm is from 0.1 to 1.5 mm.

3. A process as claimed in claim 2 in which said thickness is from 0.2 to 1 mm.

4. A process as claimed in claim 1 in which the fabric is shrunk before use.

5. A process as claimed in claim 1 in which the diaphragm is positioned as close to the cathode as possible.

6. A process as claimed in claim 1 in which the electrolyte is an aqueous solution of a chloride selected from the group consisting of sodium chloride, potassium chloride, and mixtures thereof.

7. A process as claimed in claim 6 in Which the concentration of the chloride solution is from 2 to 20%.

8. A process as claimed in claim 7 in which said concentration is from 3 to 15%.

9. A process as claimed in claim 1 in which the olefin is selected from the group consisting of a gaseous monoolefin and a halogenated monoolefin.

10. A process as claimed in claim 1 in which the olefin is selected from the group consisting of ethylene, propylene and butene.

6 References Cited UNITED STATES PATENTS 1,253,617 1/1918 McElroy 204-80 3,247,133 4/1966 Chen 260-21 3,288,692 11/1966 Leduc 204-80 JOHN H. MACK, Primary Examiner. H. M. FLOURNOY, Assistant Examiner.

US. Cl. X.R. 204-290, 296

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,451,905 Dated June 24 1969 Walter KrUnig et a1.

It is certified that an error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Colunm 4, line 28, hl" should read 4 l.

SIGNED ANU SEMED Amt:

M m. Fletcher, Ir.

Attesting Officer WILLIAM E. .SGHUYIER, JR- Oommissioner or Patenta 

